The objective of this study is to determine the response of endogenous sex hormones to varying doses of soy derived isoflavonoids in pre- and postmenopausal women. Isoflavonoids have been associated with a number of factors which could result in a decreased incidence and/or progression of breast cancer. One of these factors which has been under investigation in our laboratory is the interaction of these phytoestrogens with the circulating levels of endogenous estrogen, sex hormone binding globulin and gonadotrophins. In the first two years of the current grant cycle it has been observed that feeding soy at a single dose alters plasma and urinary estrogen and gonadotrophin levels. More than a 30% decline in urinary estrogen excretion and a 20% decline in plasma estrogen level were noted upon feeding a soy drink. In this renewal application it is proposed to study the response of female sex hormone parameters to varying levels of orally administered isoflavonoids. These data will provide information that is necessary to evaluate the minimal dose of orally administered isoflavonoids required to achieve a significant and/or maximal effect on estrogen levels in plasma and urine. The amount of isoflavonoids excreted in the urine and the concentration plasma will also be studied to determine their response to the dose of isoflavanoids ingested orally. The relationship between urinary and plasma isoflavonoid concentration over a forty fold range of orally administered isoflavonoids will be evaluated to determine if urinary values can be used as a reliable indicator of plasma levels.